CN118217552A - Correction method and device for phase change caused by ultrasonic passing through non-uniform medium - Google Patents
Correction method and device for phase change caused by ultrasonic passing through non-uniform medium Download PDFInfo
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Abstract
The invention relates to a correction method and a correction device for causing phase change when ultrasound passes through a non-uniform medium, wherein the method comprises the following steps: acquiring the position of each ultrasonic transmitting array element in an ultrasonic transducer in a photographed image; dividing an object to be processed containing a non-uniform medium into a plurality of single array element processing units according to the position of each ultrasonic transmitting array element in the shot image; respectively acquiring sound field distribution information formed after ultrasonic waves in each single-array element processing unit pass through a non-uniform medium; and carrying out phase or amplitude adjustment on the sound field distribution information of each single array element processing unit to obtain correction information of each ultrasonic transmitting array element in the ultrasonic transducer. Compared with the prior art, the ultrasonic energy-saving device can focus ultrasonic signals at the same position, so that the target area can obtain enough ultrasonic energy, and the target area does not have excessive energy accumulation.
Description
Technical Field
The invention relates to the technical field of ultrasonic emission, in particular to a correction method and device for phase change caused by ultrasonic passing through a non-uniform medium.
Background
High Intensity Focused Ultrasound (HIFU) has been widely used in therapy and surgery. The therapeutic ultrasound has a frequency in the range of 0.8MHz to 5MHz and propagates within the tissue at a wavelength of about 2mm to 0.3mm (corresponding to the frequencies described above). This means that a higher sound pressure (high intensity) can be generated in a smaller area at a focal plane at a distance from the sound source. Thus, in theory, if the ultrasound beam has sufficient energy to pass through the sound absorbing medium, it is possible to obtain a biologically significant temperature rise only in this region (focal point) while the temperature rise in other regions (non-focal regions) is negligible. Since ultrasound is a mechanical wave, there is some energy loss as the ultrasound propagates through the tissue, and in order to overcome signal losses in the tissue due to acoustic absorption and scattering, the acoustic energy may be concentrated into a small volume to obtain a focused ultrasound beam. When the ultrasound waves emitted by HIFU operation are focused deep in soft tissue, the temperature at the focus can be increased to the point where the tissue is thermally destroyed, while leaving the other tissue sites at a temperature near their original level, including the temperature of the tissue in the path of the ultrasound beam propagation above the focal volume.
To achieve the above-described focusing effect of ultrasound, a treatment probe in the form of a spherical curve, an acoustic lens, a reflector or a phased array may be used, i.e., by arranging a sound source larger than the wavelength in the ultrasound field in the form of a spherical curve, it is finally possible to focus on a point with a focal point size on the order of the wavelength. In practical application, in order to more efficiently and accurately transmit ultrasonic energy to a target area, a phased focusing ultrasonic transducer, i.e., an array type ultrasonic transducer, is selected. The ultrasonic transmitting units in the array can be independently driven, and the relative phases and the transmitting amplitudes of the units are adjusted, so that the accurate focusing of the focus of the target area and the rapid and accurate movement of focuses at different positions are realized. Visual feedback of the focus of the target area can be realized by combining a magnetic resonance image guiding technology.
When ultrasound waves pass through human tissue and apply energy to a target area within the human body, the primary purpose is to focus more energy to the target area than the target area does not pass through too much energy. However, human tissue is a non-uniform medium for ultrasound waves, and as ultrasound waves pass through the skull, variations in waveform phase occur and the coherent waveform is distorted, resulting in unintended focus in non-target areas. The above problems may lead to abnormal heating, irritation of non-target tissue, which may create a risk of unintended energy interference in the non-target. Therefore, there is a need for systems and methods that reduce non-target energy buildup while ensuring sufficient ultrasound energy at the target.
Taking ultrasound transcranial treatment as an example, when ultrasound propagates through the skull, the ultrasound propagates at a variable speed through the skull due to non-uniformity of the skull medium, which results in defocusing due to phase changes at the point where the ultrasound reaches the intracranial intended focus, as shown in fig. 1, i.e., the target area is not able to acquire enough energy, which necessarily results in an increase in energy in the non-target area.
At present, the correction methods commonly used for the ultrasonic phase change are roughly divided into two types. The first approach assumes that the skull or other non-uniform tissue consists of one or three uniform layers, and since the skull is a positive phase shift relative to water, a correction phase can be achieved by the phase shift, which can be directly adapted for clinical treatment. Although the target focusing effect can be corrected faster by using the model, the non-uniform medium characteristics of the skull extracted from the high-resolution CT image are not considered, so that the lifting effect is limited. The second approach achieves non-invasive focusing of ultrasound through the skull by modeling the non-uniform medium properties of the complete wave equation and the skull using a time reversal method and three-dimensional finite difference values. However, convergence testing has shown that a longer time is required to obtain relatively high precision results.
Disclosure of Invention
The present invention aims to overcome the above-mentioned drawbacks of the prior art by providing a correction method and apparatus for inducing a phase change in ultrasound passing through a non-uniform medium, which reduces non-target energy accumulation while ensuring sufficient ultrasound energy at the target.
The aim of the invention can be achieved by the following technical scheme:
in a first aspect of the invention, a method of modifying an ultrasound wave to cause a phase change when passing through a non-uniform medium is disclosed, comprising the steps of:
acquiring the position of each ultrasonic transmitting array element in an ultrasonic transducer in a photographed image;
Dividing an object to be processed containing a non-uniform medium into a plurality of single array element processing units according to the position of each ultrasonic transmitting array element in the shot image;
Respectively acquiring sound field distribution information formed after ultrasonic waves in each single-array element processing unit pass through a non-uniform medium;
And carrying out phase or amplitude adjustment on the sound field distribution information of each single array element processing unit to obtain correction information of each ultrasonic transmitting array element in the ultrasonic transducer.
Further, the method further comprises: feeding back the correction information of each ultrasonic transmitting array element to the ultrasonic transmitting array element; and each ultrasonic transmitting array element re-transmits ultrasonic waves to the non-uniform medium according to the correction information.
Further, the non-uniform medium is skull and/or muscle tissue and/or the captured image is a magnetic resonance, ultrasound or CT image of the skull and/or muscle tissue.
Further, the method for dividing the object to be processed containing the non-uniform medium into a plurality of single-array element processing units comprises the following steps:
Setting a virtual receiving layer, wherein the non-uniform medium is positioned between the ultrasonic transmitting array element and the virtual receiving layer;
Dividing and shooting images in a one-to-one correspondence mode according to the number of the ultrasonic transmitting array elements to obtain a plurality of single array element processing units;
each single array element processing unit comprises an ultrasonic transmitting array element, a non-uniform medium image corresponding to the ultrasonic transmitting array element and a virtual receiving layer.
Further, each virtual receiving layer corresponds to a single array element processing unit.
Further, the process of acquiring the correction information of each array element of the ultrasonic transducer array specifically includes:
Selecting a sound pressure signal at a position from the virtual receiving layer as a reference signal;
and acquiring a time delay matrix between the sound pressure signal of the corresponding position of each remaining virtual receiving layer and the reference signal, and acquiring phase correction information of the array elements of the corresponding ultrasonic transducer array based on the time delay matrix.
Further, the method for acquiring the phase correction information includes:
In the method, in the process of the invention, For the phase matrix to be corrected, f is the transmit frequency of the ultrasound transducer,N is the number of array elements in the ultrasound transducer array.
Further, the calculating process of the sound field distribution information includes: and respectively constructing a momentum conservation equation, a mass conservation equation and an object state equation in the single array element processing unit to obtain a sound wave equation set, constructing a second-order wave equation according to the equation set, and solving the second-order wave equation to obtain sound field distribution information of the virtual receiving layer.
Further, in the calculation process of the sound field distribution information, sound wave passes through the uniform lossless fluid medium to calculate the sound field distribution information;
The calculation expression of the momentum conservation equation is as follows:
In the method, in the process of the invention, The sound field is the vibration velocity of particles, p is sound pressure, ρ 0 is the static density of the medium without acoustic disturbance in the sound field, and t is time;
The calculation expression of the mass conservation equation is as follows:
Wherein ρ is the density in the sound field;
The calculation expression of the object state equation is as follows:
p＝c0 2ρ
Where c 0 is the speed of sound propagation in the medium.
Further, the second-order wave equation has a calculation expression of:
Further, the method for calculating sound field distribution information under the condition that sound waves pass through uniform lossless fluid medium comprises the following steps:
assuming a uniform lossless medium, the second order wave equation is:
By performing spatial Fourier transform and then using second-order accurate center difference pair time derivative, a pseudo spectrum solution can be obtained, namely, sound field distribution information in a virtual receiving layer:
Wherein, Is a variable of k-space,/>Δt is the time step.
Further, the distance between each virtual receiving layer and the corresponding ultrasonic transmitting array element is equal.
In a second aspect of the invention, a correction device for inducing a phase change in ultrasound passing through a non-uniform medium is disclosed, comprising a memory and a processor, said memory storing program code, the processor invoking said program code to perform the steps of the method as described above.
In a third aspect of the invention, a machine-readable storage medium is disclosed, characterized in that it has stored thereon a program code for performing the steps of the method according to any of the preceding claims by a processor.
Compared with the prior art, the invention has the following advantages:
(1) According to the invention, aiming at each array element in the ultrasonic transducer array, a single array element processing unit is respectively established at a corresponding position in an object to be processed containing a non-uniform medium, sound field distribution information of a virtual receiving layer formed after ultrasonic waves pass is calculated, so that acoustic signals are received, the acoustic signals of each single array element processing unit are subjected to calculation processing to realize phase or amplitude adjustment, the correction of the whole ultrasonic transducer array is realized, and ultrasonic signals of each array element can be focused at the same position, so that enough ultrasonic energy can be obtained in a target area, and excessive energy accumulation does not exist in the target area.
(2) According to the invention, by establishing the corresponding virtual receiving layer for each single array element processing unit, the ultrasonic signals passing through the non-uniform medium can be recorded, and unified correction among array elements is carried out, so that correction information is more accurate.
(3) The preset area is smaller, namely the area between the ultrasonic transmitting array element and the virtual receiving layer, and the efficiency is higher.
(4) The single array element processing units can independently operate without interference, and the efficiency is further improved.
Drawings
FIG. 1 is a schematic view of an ultrasound transcranial focusing state with defocus at the focus without phase correction provided in the background of the invention;
FIG. 2 is a schematic diagram of an ultrasound transcranial focusing state with defocusing at a focal point after phase correction according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a division result of a single-array element processing unit provided in an embodiment of the present invention;
Fig. 4 is a schematic diagram of an ultrasonic transmitting array element and a calculation process of receiving at a virtual receiving layer according to an embodiment of the present invention;
fig. 5 is a flow chart of a method for correcting a phase change caused by ultrasonic waves passing through a non-uniform medium according to an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
Example 1
In order to focus more energy on the target area, the embodiment proposes that the refocusing of the target area after the ultrasound transcranial can be achieved by modifying the phase of each ultrasound transmitting array element in the phased array by means of a phased ultrasound transducer, as shown in fig. 2, wherein each wafer in the transducer array is an ultrasound transmitting array element.
Specifically, the present embodiment provides a correction method for causing a phase change when ultrasound passes through a non-uniform medium, including the steps of:
acquiring the position of each ultrasonic transmitting array element in an ultrasonic transducer in a photographed image;
Dividing an object to be processed containing a non-uniform medium into a plurality of single array element processing units according to the position of each ultrasonic transmitting array element in the shot image;
Respectively acquiring sound field distribution information formed after ultrasonic waves in each single-array element processing unit pass through a non-uniform medium;
And carrying out phase or amplitude adjustment on the sound field distribution information of each single array element processing unit to obtain correction information of each ultrasonic transmitting array element in the ultrasonic transducer.
Optionally, the method further comprises: feeding back the correction information of each ultrasonic transmitting array element to the ultrasonic transmitting array element; and each ultrasonic transmitting array element re-transmits ultrasonic waves to the non-uniform medium according to the correction information so as to realize the concentration of the acoustic energy in the target area.
The non-uniform medium is non-uniform tissue such as muscle, fat, bone, organ, etc., such as skull, and the corresponding photographed image can be selected from magnetic resonance, ultrasound or CT image of non-uniform tissue such as skull, muscle, etc.
The method is mainly used for correcting the phase change caused by the ultrasonic transmitting unit/array when the ultrasonic passes through the skull (heterogeneous medium), so that the maximum energy deposition of the target area can be effectively realized in real time, and the corrected phase of the method can be obtained through simulation calculation. In the implementation process of the method, the skull information acquired by CT is divided into calculation units according to the corresponding part of each array element of the ultrasonic transducer array, as shown in FIG. 3: each dashed box is a single array element processing unit.
Optionally, as shown in fig. 4, the method for dividing the object to be processed containing the non-uniform medium into a plurality of single-array element processing units includes:
setting a virtual receiving layer, wherein a non-uniform medium is positioned between the ultrasonic transmitting array element and the virtual receiving layer;
Dividing and shooting images in a one-to-one correspondence mode according to the number of ultrasonic transmitting array elements to obtain a plurality of single array element processing units;
Each single array element processing unit comprises an ultrasonic transmitting array element, a non-uniform medium image corresponding to the ultrasonic transmitting array element and a virtual receiving layer.
The virtual receiving layer is a plane in the area where the acoustic information of the ultrasonic wave sent by the ultrasonic transmitting array element passes through the non-uniform medium. Each virtual receiving layer corresponds to a single array element processing unit.
Preferably, the distances between each virtual receiving layer and the corresponding ultrasonic transmitting array element are equal, so that the subsequent phase or amplitude correction is convenient.
Each single-array element processing unit can correspond to one or more virtual receiving layers, when the plurality of virtual receiving layers are arranged, corresponding correction information can be calculated for the virtual receiving layers with the same distance as the corresponding ultrasonic transmitting array elements, so that multiple groups of correction information of the virtual receiving layers with different distances from the corresponding ultrasonic transmitting array elements are obtained, error optimization of the correction information is carried out, and more accurate correction information is obtained for correction of the ultrasonic transmitting array elements.
Optionally, the process of acquiring the correction information of each array element of the ultrasonic transducer array specifically includes:
Selecting a sound pressure signal at a position from a virtual receiving layer as a reference signal;
And acquiring a time delay matrix between the sound pressure signal and the reference signal at the corresponding position of each remaining virtual receiving layer, and acquiring phase correction information of the array element of the corresponding ultrasonic transducer array based on the time delay matrix.
The time delay between each sound pressure signal and the reference signal is corrected, so that the unification of the phase or amplitude of the sound field distribution information of each single-array element processing unit is realized, and the concentration of the sound energy in the target area is realized.
Optionally, the method for acquiring the phase correction information includes:
In the method, in the process of the invention, For the phase matrix to be corrected, f is the transmit frequency of the ultrasound transducer,N is the number of array elements in the ultrasound transducer array.
The obtained phase is input into an ultrasonic transducer array for ultrasonic energy emission, and enough ultrasonic energy can be obtained in the target area instead of the target area without excessive energy accumulation.
Optionally, the calculating process of the sound field distribution information includes: and respectively constructing a momentum conservation equation, a mass conservation equation and an object state equation in the single array element processing unit to obtain a sound wave equation set, constructing a second-order wave equation according to the equation set, and solving the second-order wave equation to obtain sound field distribution information of the virtual receiving layer.
Optionally, in the calculation process, the sound field distribution information can be calculated under the condition that the ideal small-amplitude sound wave propagates through the uniform lossless fluid medium, and the corresponding first-order equation is as follows:
Momentum conservation equation:
Mass conservation equation:
Equation of state:
p＝c0 2ρ (3)
Wherein, The mass vibration velocity in the sound field is p, p is sound pressure, ρ is density in the sound field, ρ 0 is static density of the medium without acoustic disturbance in the sound field, and c 0 is acoustic propagation velocity in the medium. The second order wave equation can be obtained from the above equation set:
taking a second-order wave equation of a uniform lossless medium as an example, writing a finite difference form as follows:
by performing a spatial fourier transform and then using the second order exact center differential pair time derivative, a pseudo-spectral solution can be derived:
Wherein, Is a variable of k-space,/>Δt is the time step. The sound field distribution information in the virtual receiving layer can be obtained by solving the equation.
More specifically, a specific process flow of the correction method for causing phase change when the ultrasound passes through a non-uniform medium is described below, and as shown in fig. 5, the method includes the steps of:
s1: acquiring a skull CT image and transmitting the skull CT image to a system terminal;
S2: the system terminal carries out informatization processing on the image;
s3: acquiring the position of each ultrasonic transmitting array element in the ultrasonic transducer in the shot image, and dividing an object to be processed containing a non-uniform medium into a plurality of single array element processing units according to the position of each ultrasonic transmitting array element in the shot image; establishing an ultrasonic propagation computing environment of the skull region aiming at each single array element block in the ultrasonic transducer;
s4: respectively acquiring sound field distribution information formed by ultrasonic waves in each single-array element processing unit through a non-uniform medium in a corresponding virtual receiving layer;
s5: carrying out phase or amplitude adjustment on the sound field distribution information of each single array element processing unit to obtain correction information of each ultrasonic transmitting array element in the ultrasonic transducer;
s6: finally, the unified phase/amplitude information is fed back to each ultrasonic transmitting array element;
S7: and each ultrasonic transmitting array element re-transmits ultrasonic waves to the non-uniform medium according to the unified phase/amplitude information so as to realize the concentration of the acoustic energy in the target area.
The above description of the method embodiments further describes the inventive solution by means of the device embodiments.
The present embodiment also relates to a correction device for causing a phase change when ultrasound passes through a non-uniform medium, comprising a memory storing program code and a processor invoking the program code to perform the steps of the correction method for causing a phase change when ultrasound passes through a non-uniform medium as described above.
The specific content and the beneficial effects of the device of the present application can be found in the above method embodiments, and are not described herein.
In addition, the present embodiment also relates to a machine-readable storage medium having stored thereon a program code for causing a processor to execute the steps of the correction method of causing a phase change when ultrasound passes through a non-uniform medium as described above.
Program code for carrying out methods of the present invention may be written in any combination of one or more programming languages. These program code may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus such that the program code, when executed by the processor or controller, causes the functions/operations specified in the flowchart and/or block diagram to be implemented. The program code may execute entirely on the machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.
In the context of the present invention, a machine-readable storage medium may be a tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable storage medium may be a machine-readable signal medium or a machine-readable storage medium. The machine-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of a machine-readable storage medium would include an electrical connection based on one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.
The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.
Claims (14)
1. A method of modifying an ultrasound wave to cause a phase change when passing through a non-uniform medium, comprising the steps of:
acquiring the position of each ultrasonic transmitting array element in an ultrasonic transducer in a photographed image;
Dividing an object to be processed containing a non-uniform medium into a plurality of single array element processing units according to the position of each ultrasonic transmitting array element in the shot image;
Respectively acquiring sound field distribution information formed after ultrasonic waves in each single-array element processing unit pass through a non-uniform medium;
And carrying out phase or amplitude adjustment on the sound field distribution information of each single array element processing unit to obtain correction information of each ultrasonic transmitting array element in the ultrasonic transducer.
2. The method of modifying an ultrasound wave that causes a phase change when passing through a non-uniform medium of claim 1, further comprising: feeding back the correction information of each ultrasonic transmitting array element to the ultrasonic transmitting array element; and each ultrasonic transmitting array element re-transmits ultrasonic waves to the non-uniform medium according to the correction information.
3. The method of claim 1, wherein the non-uniform medium is skull and/or muscle tissue and/or the captured image is a magnetic resonance, ultrasound or CT image of the skull and/or muscle tissue.
4. The method for correcting for phase change caused by ultrasonic waves passing through a non-uniform medium according to claim 1, wherein said method for dividing an object to be processed containing a non-uniform medium into a plurality of unit cell processing units comprises:
Setting a virtual receiving layer, wherein the non-uniform medium is positioned between the ultrasonic transmitting array element and the virtual receiving layer;
Dividing and shooting images in a one-to-one correspondence mode according to the number of the ultrasonic transmitting array elements to obtain a plurality of single array element processing units;
each single array element processing unit comprises an ultrasonic transmitting array element, a non-uniform medium image corresponding to the ultrasonic transmitting array element and a virtual receiving layer.
5. The method of claim 4, wherein each of the virtual receiving layers corresponds to a single element processing unit.
6. The method for correcting phase change caused by ultrasonic waves passing through a non-uniform medium according to claim 4, wherein the process of obtaining correction information of each array element of the ultrasonic transducer array specifically comprises:
Selecting a sound pressure signal at a position from the virtual receiving layer as a reference signal;
and acquiring a time delay matrix between the sound pressure signal of the corresponding position of each remaining virtual receiving layer and the reference signal, and acquiring phase correction information of the array elements of the corresponding ultrasonic transducer array based on the time delay matrix.
7. The method for correcting for phase change caused by ultrasonic waves passing through a non-uniform medium according to claim 6, wherein said method for acquiring phase correction information comprises:
In the method, in the process of the invention, For the phase matrix to be corrected, f is the transmit frequency of the ultrasound transducer,N is the number of array elements in the ultrasound transducer array.
8. The method of claim 1, wherein the calculating of the sound field distribution information comprises: and respectively constructing a momentum conservation equation, a mass conservation equation and an object state equation in the single array element processing unit to obtain a sound wave equation set, constructing a second-order wave equation according to the equation set, and solving the second-order wave equation to obtain sound field distribution information of the virtual receiving layer.
9. The method for correcting phase change caused by ultrasonic waves passing through a non-uniform medium according to claim 8, wherein in the calculation of the sound field distribution information, the sound field distribution information is calculated with sound waves passing through a uniform non-destructive fluid medium;
The calculation expression of the momentum conservation equation is as follows:
In the method, in the process of the invention, The sound field is the vibration velocity of particles, p is sound pressure, ρ 0 is the static density of the medium without acoustic disturbance in the sound field, and t is time;
The calculation expression of the mass conservation equation is as follows:
Wherein ρ is the density in the sound field;
The calculation expression of the object state equation is as follows:
p＝c0 2ρ
Where c 0 is the speed of sound propagation in the medium.
10. The method of claim 9, wherein the second order wave equation is calculated by:
11. The method for correcting for phase changes caused by ultrasonic waves passing through a non-uniform medium according to claim 10, wherein said method for calculating sound field distribution information in the case of passing through a uniform non-destructive fluid medium with sound waves comprises:
assuming a uniform lossless medium, the second order wave equation is:
By performing spatial Fourier transform and then using second-order accurate center difference pair time derivative, a pseudo spectrum solution can be obtained, namely, sound field distribution information in a virtual receiving layer:
Wherein, Is a variable of k-space,/>Δt is the time step.
12. The method of claim 4, wherein the distances between each virtual receiving layer and the corresponding ultrasound transmitting array element are equal.
13. A correction device for inducing a phase change in ultrasound passing through a non-uniform medium, comprising a memory and a processor, the memory storing program code, the processor invoking the program code to perform the steps of the method of any of claims 1 to 12.
14. A machine readable storage medium having stored thereon program code for performing the steps of the method according to any of claims 1 to 12 by a processor.
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| Publication Number | Publication Date |
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| CN118217552A true CN118217552A (en) | 2024-06-21 |
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